Control system for two cycle direct injection engine and the method thereof

ABSTRACT

Disclosed is a control system and method of a two cycle direct fuel injection engine capable of smoothly suspending combustions in the cylinder during light load operation of the engine. Based on a map parameterizing the engine speed and the target engine load, it is judged whether or not, when the engine load is in the light load condition, the target engine load is located in a suspending area in which misfires tend to occur. If the target engine load is not in the suspending area, since there is no possibility of misfire, the normal combustion cycle is continued to operate. On the other hand, if the target engine load enters into the suspending area, the control system instructs the fuel injection and ignition apparatuses so as to suspend fuel injection and spark ignition with a frequency determined according to the magnitude of the engine load. The frequency is determined by a predetermined formula such that it is reduced as the engine load becomes high and is increased as the engine load becomes low.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control system and method of a twocycle direct fuel injection engine and more particularly to an enginecontrol system and method capable of eliminating misfires and improvingcombustion by means of suspending fuel injection and ignitionperiodically.

2. Prior Arts

In conventional port scavenging two cycle engines, generally the amountof residual gas versus to the amount of fresh air increases in the lightloading condition and consequently misfires tend to occur cyclically inthe cylinder. As a result of this, excessive emissions of unburnedhydrocarbons contributing to poor fuel economy are produced.

Miscellaneous techniques to solve these problems have been proposed.Among them, the stratified charge combustion techniques in which fuel isdirectly injected into cylinders and burned in the stratified manner areeffective to prevent misfiring. The conditions to realize the stratifiedcharge combustion are not simple, namely conditions such as the shape ofthe combustion chamber, the state of fuel spray, the state of gas flow,miscellaneous control values and the like are needed to put into goodtrim. However, it is generally difficult to realize homogeneouscombustion in the high speed and high load conditions with theseconditions retained. Especially in case of small engines with a highspecific power, these conditions to realize the stratified chargecombustion are difficult to be satisfied.

Therefore, in order to prevent misfires under light load conditions,other techniques than the stratified charge combustion must be chosen.Thus, it is considered to reduce combustion cycles, namely to suspendcombustions selectively in the light load condition where misfires tendto occur. By selectively suspending combustions, it is possible toassure a good scavenging in a cycle wherein combustion is suspended andto assure a good combustion in a cycle wherein combustion is undertaken.

As techniques of suspending combustions, for example, Japanese PatentApplication Toku-Kai-Sho 62-157259 discloses a technique of selectivelysuspending fuel injections for a diesel engine and Japanese PatentApplication Toku-Kai-Sho 59-65526 also discloses a technique ofselectively suspending fuel injections for a port injection typefour-cycle engine.

However, in a two cycle direct fuel injection engine, no specifictechnique of selectively suspending fuel injection has ever beendisclosed. Therefore, it is now expected that a two cycle direct fuelinjection engine capable of smoothly controlling combustions in lightload conditions will be developed.

SUMMARY OF THE INVENTION

It is, therefore in view of the above situations, an object of thepresent invention to provide a control system for a two cycle incylinder fuel injection engine capable of reducing hydrocarbon emissionsand of improving fuel economy.

It is another object of the invention to provide a combustion controlsystem capable of applying to an actual two-cycle in cylinder fuelinjection engine easily, securedly and with low cost.

To achieve these objects, the control system according to the presentinvention comprises:

target load detecting means for detecting an engine load targeted by anengine operator;

engine speed detecting means for detecting an engine speed;

mapping means for mapping a suspending area where-in fuel injection andsaid spark ignition are to be suspended;

suspending control judging means for judging whether or not the engineload parameterizing the engine speed is located in the suspending area;

suspending frequency determining means when the engine loadparameterizing the engine speed is located in the suspending area fordetermining a frequency of suspending fuel injection and spark ignitionso as to reduce the frequency with an increase of the engine load;

injection suspending means for suspending fuel injection according tothe frequency; and

ignition suspending means for suspending fuel injection according to thefrequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of an electronic control unitaccording to a first embodiment of the present invention;

FIG. 2 is a schematic diagram showing an engine control system accordingto a first embodiment of the present invention;

FIG. 3 is a flowchart showing a suspending control according to a firstembodiment of the present invention;

FIG. 4 is a diagram showing a suspending control area according to afirst embodiment of the present invention;

FIGS. 5a-5c are examples of charts for calculating cycles of suspendingcombustion according to a first embodiment of the present invention;

FIG. 6 is a schematic diagram showing an engine control system accordingto a second embodiment of the present invention;

FIG. 7 is a functional block diagram of an electronic control unitaccording to a second embodiment of the present invention;

FIG. 8 is a flowchart showing a suspending control according to a secondembodiment of the present invention;

FIG. 9 is a flowchart continued from FIG. 8;

FIG. 10 is a timing chart showing an example of a suspending controlaccording to a second embodiment of the present invention;

FIG. 11 is a functional block diagram of an electronic control unitaccording to a third embodiment of the present invention;

FIG. 12 is a flowchart showing a suspending control according to a thirdembodiment of the present invention;

FIG. 13 is a schematic diagram showing a relationship between the numberof suspending and an injection amount according to a third embodiment ofthe present invention;

FIG. 14 is a schematic diagram showing a relationship between a numberof suspending and an ignition timing according to a third embodiment ofthe present invention;

FIG. 15 is a schematic diagram showing an engine control according to afourth embodiment of the present invention;

FIG. 16 is a functional block diagram of an electronic control unitaccording to a fourth embodiment of the present invention;

FIG. 17 is a flowchart for determining a starting point of suspendingcombustions according to a fourth embodiment of the present invention;

FIG. 18 is a schematic diagram showing an engine control systemaccording to a fifth embodiment of the present invention;

FIG. 19 is a functional block diagram of an electronic control unitaccording to a fifth embodiment of the present invention;

FIG. 19A is a functional block diagram of a modification wherein thefourth embodiment is combined with the fifth embodiment;

FIG. 20 is a flowchart for determining a starting point of suspendingcombustions according to a fifth embodiment of the present invention;and

FIG. 21 is a diagram showing a relationship between the fuel propertiesand a starting point of suspending combustions.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 2, numeral 1 denotes a two-cycle in-cylinder fuelinjection engine in which fuel is directly injected into cylinders and afuel mixture gas is burned by spark ignition. The intake system of theengine 1 is equipped with a throttle body 2 incorporating a throttlevalve therein and an air cleaner 3 is disposed upstream of the throttlebody 2. On the other hand, in the exhaust system of the engine 1 thereis provided with a catalytic converter 4 for purifying exhaust gases anddownstream of the catalytic converter 4 there is provided with a muffler5.

In the combustion chamber of the engine 1 there are provided with a fuelinjector 6 for directly injecting high pressure fuel thereinto and aspark plug 7. The spark plug 7 is connected with the secondary windingside of an ignition coil 8 and an igniter 9 driven by an electroniccontrol unit (ECU) 20 for engine control is connected with the primaryside of the ignition coil 8.

The ECU 20 comprises a CPU 21, a ROM 22 for storing a control program,miscellaneous maps and fixed data, a RAM 23 for storing miscellaneousprocessed data, an input interface 24 to which signals of sensors fordetecting engine conditions are inputted, an output interface 25 foroutputting control signals of the CPU 21 to miscellaneous actuators anda bus line 26 for connecting these devices with each other.

The input interface 24 is connected with a throttle opening angle sensor10 incorporated in the throttle body 2 for detecting an opening angle ofthe throttle valve, a crank angle sensor 11 for detecting a crank angleof the engine 1 and a fuel pressure sensor 12 for detecting a fuelpressure of the high pressure line in the fuel system.

On the other hand, the output interface 25 is connected with the igniter9 and the fuel injector 6 through a drive circuit 27.

In the CPU 21, miscellaneous control values such as a fuel injectionamount, an ignition timing and the like are calculated based upon themiscellaneous data stored in the RAM 23 according to the control programstored in the ROM 22 and these control values are outputted to theinjector 6 and the igniter 9 so as to maintain the engine 1 in theoptimal condition.

That is to say, when the engine load stays at the low load conditionwherein misfires tend to occur, the frequency of suspending combustionsis determined in accordance with the magnitude of the engine load andsignals for suspending combustions are outputted to the fuel injector 6and the igniter 9. The frequency of suspending combustions is controlledby calculations which will be described in detail hereinafter in such away that the suspending of combustions increases as the engine loadbecomes large and decreases as the engine load becomes small.

In order to realize the above cycle control, as indicated in FIG. 1, theECU 20 comprises an engine speed calculating section 31, a crankposition detecting section 32, an operating conditions detecting section33, a suspending control judging section 34, a suspending conditions map35, an injection/ignition determining section 36, an injection amountdetermining section 37, a corrected injection timing determining section38, a corrected ignition timing determining section 39, an injectiontiming determining section 40, an ignition timing determining section 41and driver sections 42, 43.

The engine speed calculating section 31 calculates an engine speed N_(E)based on signals derived from the crank angle sensor 11, that is, thecrank angle sensor 11 and the engine speed calculating section 31constitutes engine speed detecting means. Further, the crank positiondetecting section 32 detects a crank angle based on signals derived fromthe crank angle sensor 11.

The operating conditions detecting section 33 is for detecting an engineload corresponding to a throttle opening angle α based on signals fromthe throttle sensor 10. That is, the throttle opening angle sensor 10and the operating conditions detecting section 33 constitute a targetengine load detecting means. Further, in this operating conditionsdetecting section 33, a reference delivery ratio L_(O) is determined byreferring to a predetermined table parameterizing the throttle openingangle α and the engine speed N_(E). An optimal reference delivery ratioL_(O) corresponding to the combination of the throttle opening angle αand the engine speed N_(E) is prepared beforehand by experiments and isstored on a specific area of that table.

In the suspending control judging section 34, it is judged whether ornot a target load required by an engine operator is located in apredetermined suspending area (an area in which the suspending ofcombustions is to be performed by suspending fuel injection andignition) by referring to the suspending conditions map 35parameterizing the engine load detected by the operating conditiondetecting section 33 and the engine speed N_(E) calculated in the enginespeed calculating section 31.

The above suspending conditions map 35 is, as shown in FIG. 4, a mapparameterizing the engine load and the engine speed N_(E), which isobtained based on experiments or the like. The suspending area is anarea below a suspending line which is drawn slightly higher than an areaobtained from actual experiments.

In the injection/ignition determining section 36, based on signalsderived from the suspending control judging section 34, it is determinedwhether the subject cycle is a combustion cycle or is a suspending cycleand that signal is outputted to the fuel injection amount determiningsection 37, the corrected fuel injection determining section 38 and thecorrected ignition timing determining section 39. When it is determinedthat the subject cycle is a combustion cycle, fuel injection and sparkignition are performed respectively once per one engine revolution.Further, when it is determined that the subject cycle is a suspendingcycle, the frequency of the suspending cycle is determined so as toincrease as the engine load becomes low and to decrease as the engineload becomes high.

Further, in the fuel injection amount determining section 37, a fuelinjection amount GF is determined by referring to a table parameterizingthe reference delivery ratio L_(O) and the engine speed N_(E). Further,a fuel pressure coefficient K_(s) and a dead fuel injection time T_(s)are determined by referring to a table parameterizing a fuel pressureP_(s) of the fuel pressure in the high pressure line of the fuel system.The abovementioned tables have been prepared by experiments or throughdesigning beforehand with respect to corresponding parameters. The fuelpressure coefficient K_(s) is a fuel injection characteristic of thefuel injector 6, which varies according to the fuel pressure P_(s) andthe dead fuel injection time T_(s) is for compensating a delay time ofoperation of the fuel injector 6, which varies according to the fuelpressure P_(s).

The fuel injection duration time T_(i) is calculated in accordance withthe formula T_(i) =K_(s) ×GF+T_(s). and outputted to the corrected fuelinjection timing determining section 38 and the fuel injection timingdetermining section 40. When a signal for suspending combustions isinputted from the injection/ignition determining section 36, theduration time T_(i) is set to 0 (zero) and this value is outputted tothe corrected injection timing determining section 38 and the fuelinjection timing determining section 40.

In the corrected fuel injection timing determining section 38, thecorrected fuel injection timing is determined by way of making acorrection of the fuel injection timing (expressed in a crank angle)obtained from a table parameterizing the reference delivery ratio L_(O)and the engine speed N_(E) by using the necessary correction value(retard or advance expressed in a crank angle) and is outputted to theignition timing determining section 40. Further, when a signal forsuspending combustions is inputted to the corrected fuel injectiontiming determining section 38 from the injection/ignition determiningsection 36, the determination of fuel injection timing is not performed.

Further, in the fuel injection timing determining section 40, the fuelinjection timing inputted from the corrected fuel injection timingdetermining section 38 is converted into the fuel injection timing withrespect to a reference crank angle detected by the crank positiondetecting section 32 and a signal corresponding to the fuel injectionamount which is obtained from the fuel injection amount determiningsection 37 is outputted to the fuel injector 6 through the driversection 42.

Thus, a fuel injection means is constituted by the fuel injection amountdetermining section 37, the corrected fuel injection timing determiningsection 38, the fuel injection timing determining section 40, the driversection 42 and the fuel injector 6, as described above.

Further, in the corrected ignition timing determining section 39, acorrected ignition timing IG_(t) is determined by means of making acorrection by employing a correction value parameterizing the referencedelivery ratio L_(O) and the engine speed N_(E) or by means of makingother necessary corrections and is outputted to the ignition timingdetermining section 41. When a signal for suspending combustions incylinders is inputted from the injection/ignition determining section 36to this corrected ignition timing determining section 39, thedetermination of ignition timing is stopped.

Further, in the ignition timing determining section 41, the ignitiontiming outputted from the corrected ignition timing determining section39 is converted into an ignition timing with respect to a referenceposition of the crank shaft detected in the crank position detectingsection 32 and a signal of that ignition timing is outputted to theigniter 9 through the driver section 43.

Thus, an igniting means is constituted by the corrected ignition timingdetermining section 39, the ignition timing determining section 41, thedriver section 43 and the igniter 9.

Next, referring to a flowchart of FIG. 3, the suspending control of theECU 20 will be described.

First, at a step 101 (hereinafter, referred to as S number) theoperating condition of the engine, i.e., the engine speed N_(E) detectedby the engine speed calculating section 31 and the engine load detectedby the operating condition detecting section 33, is detected and at S102the suspending conditions map 35 is looked up parameterizing the enginespeed N_(E) and the engine load. Then, if the value parameterizing theengine speed N_(E) and the engine load is located above the suspendingline, since the value does not belong to a misfiring area, the normalcycle control (one injection and one ignition per one engine revolution)is performed and then the program goes out of the routine. On the otherhand, the value parameterizing the engine speed N_(E) and the engineload is located below the suspending line, since the value belongs to amisfiring area, the program goes to S103 from which the suspendingcontrol of fuel injection and spark ignition is started.

At S103, a load index X (a degree of the engine load) at the enginespeed N_(E) is determined. Namely, the engine load at the engine speedN_(E) is divided by N (integer) and it is determined where the loadindex X of the current engine load is positioned between X=1 and X=N.Here, for example, X=1 denotes an engine load at idling and X=N denotesan engine load at the point below which the suspending of combustions isstarted.

Then, the program goes to S104 where it is judged whether or not thecycle number i is 0 in order to confirm whether the present cycle is aninitial cycle for performing the suspending control, or not. If it is aninitial one (i=0), the program steps to S106 where an operator d(i=0) islet to be 0 (zero) and skips to S108. On the other hand, the cyclenumber i is not 0 (i=1, 2, 3, . . . ), the program steps to S105 wherethe operator d(i) is obtained from the following formula:

    d(i)=d(i-1)-X/N+M                                          (1)

where d(i) is an operator at the present cycle, d(i-1) is an operator atthe previous cycle, and M is an indicator for r indicating the executionof injection/ignition (M=1 denotes that an injection/ignition has beenexecuted and M=0 denotes that no injection/ignition has not beenexecuted).

After the operator d(i) is obtained from the formula (1), the programgoes to S107 where it is judged whether or not d(i) is equal to orsmaller than 0. If d(i)≦0, the program goes to S108 and if d(i)>0, itgoes to S110. When the program goes to S108 from S106 or S107, a signalis outputted from the injection/ignition determining section 36 to theinjection amount determining section 37 and the corrected injectiontiming determining section 38 so as to inject fuel at the present cycle("i"th cycle), and a signal is outputted to the corrected ignitiontiming determining section 39 so as to ignite spark at the present cycle("i"th cycle). Then, the program goes to S109 in which the indicator Mis set to 1.

On the other hand, when the program goes from S107 to S110, at S110 asignal is outputted from the injection/ignition determining section 36to the injection amount determining section 37 and the correctedinjection timing determining section 38 so as to suspend fuel injectionat the present cycle ("i"th cycle) and at the same time a signal isoutputted to the corrected ignition timing determining section 39 so asto suspend ignition at the present cycle ("i"th cycle). After that, theprogram goes to S111 where M is set to 0 (zero). When the program goesto S112 after setting M at S109 or S111, the cycle number i is countedup and this new number i is used for the next suspending control of fuelinjection and spark ignition. At S113, the operating conditions (enginespeed N_(E) and engine load) are detected and at S114 if it is judgedthat the value parameterizing the engine speed N_(E) and the engine loadis above the suspending line, the program goes out of the routine. If itis judged that that value is below the suspending line, the program goesto S115 where the new load index X is determined and then the programreturns to S105. Thus, the routine is repeated in the same manner. Whenthe program goes out of the routine from the S102 or S114, the cyclenumber i is cleared into 0.

Next, several examples of calculation of the suspending cycle will beshown with reference to FIG. 5a, FIG. 5b and FIG. 5c.

Where N is 500 and X is 255 in an example shown in FIG. 5a, since theindicator M is 1 because of the first cycle, the formula (1) is:

    d(1)=d(0)-255/500+1=0-255/500+1=245/500>0

Accordingly, the program goes to S110 where the suspending of fuelinjection and spark ignition is executed and at S111 M is set to 0.Further, at the next cycle i=2

    d(2)=d(1)-255/500+0=245/500-255/500=-10/500≦0

As a result, the program goes to S108 where fuel injection and sparkignition is executed, and at S109 M is set to 1. At the subsequentcycles, the third cycle, the fourth cycle . . . , the calculations willbe executed in the same manner. In this case, the suspending of fuelinjection and spark ignition is performed alternately.

On the other hand, referring to an example shown in FIG. 5b, where N is500 and X is 400 (the load is located on the higher side within thesuspending area), the suspending of fuel injection and spark ignitionappears every five cycles.

Further, referring to an example shown in FIG. 5c, where N is 500 and Xis 100 (the load is located on the lower side within the suspendingarea), the fuel injection and spark ignition appears every five cycles.

That is to say, according to the formula (1), the value parameterizingthe engine speed and the engine load is located in the suspending area,the frequency of the suspending of combustion is controlled so as to belower as the target engine load is higher.

Thus, according to the first embodiment of the two-cycle directinjection engine, misfires can be prevented by suspending combustions atthe frequency corresponding to the engine load. That is to say, when theengine load is at the area where misfire tends to occur, the scavengingis performed securedly at cycles without combustion and the combustionis performed securedly at cycles with combustion, whereby excessivehydrocarbons emissions and poor fuel economy being prevented.Furthermore, since the frequency of suspending combustions is determinedproperly according to the degree of the engine load, the combustioncontrol can be easily and smoothly accomplished.

Next, a second embodiment according to the present invention will bedescribed with reference to FIG. 6, FIG. 7, FIG. 8, FIG. 9 and FIG. 10.In this embodiment, the engine is a multi-cylinder engine wherein thesuspending control is independent for a specific cylinder.

Referring to FIG. 6, numeral 50 is a two-cycle spark ignitionmulti-cylinder direct injection engine and in this embodiment the engineis a three cylinder engine. In the engine 50, in addition to thecomponents of the engine 1 according to the first embodiment, a cylinderdiscrimination sensor 13 is equipped with the engine 50. The cylinderdiscrimination sensor 13 is for discriminating the cylinder numbersubjected to fuel injection and ignition and it is connected with theinput interface 24 of the ECU 51.

The object of the second embodiment is to prevent such a situation thata specific cylinder is always subjected to the suspending of combustionand another cylinder is always subjected to combustion. In the cyclecontrol of this engine, when the target load (the present position ofthe throttle opening angle) is located at the area where misfires tendto occur, the suspending control is performed separately for eachcylinder. That is to say, for example, when in the #1 cylinder it isjudged that the target load is at the suspending area, the suspendingcontrol is performed according to the signals of fuel injection andignition for #1 cylinder based on a signal of the cylinderdiscrimination sensor 13 and then in the #3 cylinder the suspendingcontrol is performed according to the signals fuel injection andignition for #3 cylinder. The frequency of suspending is determinedindependently for each cylinder according to the degree of the engineload in the same manner as in the first embodiment.

In order to realize the above cycle control, the ECU 51 mainlycomprises, as shown in FIG. 7, an engine speed calculating section 31, acrank position detecting section 52, an operating condition detectingsection 33, a suspending control judging section 53, a suspendingconditions map 35, an injection/ignition determining section 54, aninjection amount determining section 37, a corrected injection timingdetermining section 38, corrected ignition timing determining section39, an injection timing determining section 40, an ignition timingdetermining section 41, and driver sections 42, 43.

The crank position detecting section 52 detects a crank angle for eachcylinder based on a signal derived from the crank angle sensor 11 and asignal derived from the cylinder discriminating sensor 13. Thus, acylinder discriminating means is constituted by the crank angle sensor11 and the cylinder discriminating sensor 13.

Further, the suspending control judging section 53 judges whether or notthe engine load detected by the operating condition detecting section33, namely the target engine load required through the throttle valve islocated in the suspending area by referring to the suspending conditionmap 35 parameterizing the engine speed N_(E) calculated by the enginespeed calculating section 31 and the engine load detected by theoperating condition detecting section 33.

If the target engine load is not located in the suspending area, sincethere is no possibility of misfiring, each cylinder is controlledindependently so as to perform one injection and one ignition per oneengine revolution. On the other hand, when the target engine load is inthe suspending area, the frequency of suspending fuel injection andignition is determined according to the predetermined formula so as toreduce the frequency of suspending fuel injection and spark ignition asthe target load becomes high and this determination signal is outputtedto the injection/ignition determining section 54.

Next, in the injection/ignition determining section 54, based on thatdetermination signal, it is determined independently for each #1, #2 and#3 cylinder that the present cycle is subjected to either a suspendingcycle or a combustion cycle and the determination signal is outputted tothe injection amount determining section 37, the corrected injectiontiming determining section 37, and the corrected ignition timingdetermining section 39.

Next, the suspending control according to the second embodiment will bedescribed with reference to the flowcharts shown in FIG. 8 and FIG. 9.

Referring now to FIG. 8, as described in the first embodiment, at S101the engine speed N_(E) and the engine load are detected and at S102 whenit is judged that the value parameterizing the engine speed N_(E) andthe engine load is below the suspending line and there is a possibilityof misfiring at low load cycles, the program goes to S103 where the loadindex X of the engine load is determined and then the program steps toS201. The steps after S201 are those which are executed per eachcylinder independently.

At S201, it is judged whether or not the present cycle is a first one(cycle number i=0) for the #k cylinder (k=1, 2 and 3). If it is thefirst one, the program steps to S203 where an operator d_(k) (0)for the#k cylinder is set to 0 and the program skips to S205. On the otherhand, if the cycle number i is equal to or larger than 1 (i=1, 2, 3, . .. ), the program goes to S202 where the operator d_(k) (i) for the #kcylinder at the cycle number i is obtained from the following formula:

    d.sub.k (i)=d.sub.k (i-1)-X/N+M.sub.k                      (2)

where d_(k) (i-1) is an operator for the #k cylinder at the previous i-1cycle; M_(k) is an indicator for the #k cylinder which has beendetermined at the previous cycle.

After the operator d_(k) (i) for the #k cylinder is obtained from theabove formula (2), the program goes to S204 where it is judged whetheror not the obtained operator d_(k) (i) is equal to 0 or smaller than 0(d_(k) (i)≦0). If d_(k) (i)≦0, the program goes to S205 and if d_(k)(i)>0, the program takes a step to S207.

When the program steps from S203 or S204 to S205, a signal is outputtedfrom the injection/ignition determining section 54 to the correctedinjection amount determining section 37 and the corrected ignitiontiming determining section 38 so as to inject fuel into the #k cylinderand at the same time a signal is outputted from the injection/ignitiondetermining section 54 to the corrected ignition timing determiningsection 39 so as to apply a spark ignition to the #k cylinder. Afterthat, at S206 the indicator M_(k) is set to 1.

On the other hand, when the program goes from S204 to S207, in which asignal is outputted from the injection/ignition determining section 54so as to suspend a fuel injection and at the same time a signal isoutputted from the injection/ignition determining section 54 to thecorrected ignition timing determining section 39 so as to suspend aspark ignition to the #k cylinder. Then, the program goes to S208 wherethe indicator M_(k) is set to 0.

After setting the indicator M_(k) at S206 or S208, the program steps toS209 where the cycle number i of the #k cylinder is counted up and thenat S210 the operating conditions (engine speed N_(E) and engine load)are detected. Then, at S211 it is judged whether or not the valueparameterizing the engine speed N_(E) and the engine load is located inthe area where misfires tend to occur by referring to the suspendingconditions map 35 parameterizing the engine speed N_(E) and the engineload. If it is judged that the value is not in the area where misfirestend to occur, the program goes out of the routine because this cycle isa normal combustion cycle. On the other hand, if it is judged that thevalue is in the area where misfires tend to occur, the program steps toS212 in which the load index X of the target engine load is graded inthe resolution N at the engine speed N_(E) and then returns to S202 fromwhich the same routine is repeated. When the program goes out of theroutine, the cycle number i of the #k cylinder is cleared into 0.

FIG. 10 shows an example of a time chart of the aforementionedsuspending control. In this example, for the #1 cylinder a combustionand a suspending of fuel injection and ignition and an execution of fuelinjection and ignition are executed interchangeably according to theaforementioned flowchart. Also, in the #2 and #3 cylinders, thesuspending control is performed respectively in the similar way.

According to the second embodiment, the same effect as described in thefirst embodiment can be obtained for each #1, #2 and #3 cylinder.Additionally, according to the second embodiment, since the suspendingcontrol is made independently for each cylinder, the impartiality ofcombustions among cylinders can be prevented. That is to say, in casewhere the first embodiment is applied to a three cylinder two cycleengine, for example, when a suspending of combustion is attempted to beexecuted every three cycles, a specific cylinder is all the timesubjected to suspendings of combustion and other two cylinders are allthe time subjected to combustions. This impartiality of combustionsresults in causing abnormal vibrations and noises during the operationof the engine.

FIG. 11, FIG. 12, FIG. 13 and FIG. 14 show a third embodiment accordingto the present invention. According to the third embodiment, when it isjudged that the target load is located in the suspending area, the fuelinjection amount and the ignition timing are corrected in accordancewith the number of suspending. Since the constitution of the enginecontrol system of the third embodiment is roughly the same as that ofthe second embodiment, the same numerals are attached to the samesections as described in the second embodiment.

Referring now to FIG. 11, numeral 60 denotes an ECU in which, when thetarget load is located in the area where misfires tend to occur, thefrequency of suspending combustions is determined by use of a formulaindependently for each #1, #2 and #3 cylinder based on the engine speedand the engine load so as to reduce that frequency as the engine loadbecomes high. After thus determined frequency is converted into asignal, the signal is outputted to the fuel injection and ignitionsystems to suspend fuel injection and spark ignition for that cycle. Onthe other hand, the number of suspending has been counted independentlyfor each cylinder and in the next combustion cycle the fuel injectionamount and the ignition timing are corrected in accordance with thatnumber of the previous suspendings. The corrected fuel injection amountand the corrected ignition timing are converted into signalsrespectively and those signals operate the fuel injection and ignitionsystems so as to drive the injector 6 and the igniter 9.

To realize the above cycle control, the ECU 60 mainly comprises anengine speed calculating section 31, a crank position detecting section52, an operating condition detecting section 33, a suspending controljudging section 61, a suspending conditions map 35, aninjection/ignition determining section 54, an injection amountdetermining section 62, an injection amount correcting section 63, acorrected fuel injection timing determining section 38, acorrected-ignition timing determining section 64, an ignition timingcorrecting section 65, an injection timing determining section 40, anignition timing determining section 41 and driver sections 42, 43.

The suspending control judging section 61 judges whether or not theengine load detected by the operating condition detecting section 33,namely the target engine load required through the throttle valve islocated at the suspending area by referring to the suspending conditionmap 35 parameterizing the engine speed N_(E) calculated by the enginespeed calculating section 31 and the engine load detected by theoperating condition detecting section 33.

If the target engine load is not located in the suspending area, sincethere is no possibility of misfiring, each cylinder is controlledindependently so as to execute one injection and one ignition per oneengine revolution. On the other hand, when the target engine load is inthe suspending area, the frequency of suspending fuel injection andignition is determined according to the predetermined formula so as toreduce the frequency of suspending fuel injection and spark ignition asthe target load becomes high and this determination signal is outputtedto the injection/ignition determining section 54. Further, in thesuspending control judging section 61, based on a signal derived fromthe injection/ignition determining section 54, the number of suspendingis counted independently for each cylinder and is outputted to theinjection amount correcting section 63 and the ignition timingcorrecting section 65.

In the injection amount determining section 62, the fuel injectionamount GF is determined for each cylinder by referring to the tableparameterizing the reference delivery ratio L_(O) detected by theoperating condition detecting section 33 and the engine speed N_(E) fromthe engine speed calculating section 31 and further the fuel pressurecoefficient K_(s) and the dead fuel injection time T_(s) are determinedby referring to the table parameterizing the fuel pressure Ps detectedby the fuel pressure sensor 12. Further, the final fuel injection amountis converted into the fuel injection duration time T_(i). The fuelinjection duration time T_(i) is calculated in accordance with theformula T_(i) =K_(s) ×GF+T_(s) and outputted to the corrected fuelinjection timing determining section 38 and the fuel injection timingdetermining section 40.

Further, when the signal for suspending combustion is inputted from theinjection/ignition determining section 54 to the fuel injection amountdetermining section 62, the fuel injection duration time T_(i) is set to0 and this value is outputted to the corrected injection timingdetermining section 38 and the injection timing determining section 40.

On the other hand, when a signal for instructing injection during thesuspending control is inputted from the injection/ignition determiningsection 54 to the injection amount determining section 62, T_(i) is setto the fuel injection amount at the minimum load on the suspending lineand an increment correction coefficient K_(MS) for increasing the fuelinjection amount at the suspending control is read from the injectionamount correcting section 63. The final fuel injection amount isobtained by correcting the above T_(i) by this increment. Correctioncoefficient K_(MS) (T_(i) +K_(MS)) and this value is outputted to thecorrected injection timing determining section 38 and the injectiontiming determining section 40. The fuel injection amount at the minimumload on the suspending line has been stored beforehand as the dataparameterizing the engine speed N_(E) .

In the injection amount correcting section 63, the increment correctioncoefficient K_(MS) is stored on a map parameterizing the number ofsuspendings which is inputted from the suspending control judgingsection 61 and is read by the injection amount determining section 62.The map is prepared beforehand through experiments and the like. Theincrement correction coefficient K_(MS) has a characteristic rising withan increase of the number of suspendings as shown in FIG. 13 so as toshift the air-fuel (A/F) slightly to the rich side-as the number ofsuspendings increases.

Thus, the injection amount determining section 62, the injection amountcorrecting section 63, the corrected injection timing determiningsection 38, the injection timing determining section 40, the driversection 42 and the injector 6 constitute a fuel injection meansaccording to the third embodiment.

Further, in the corrected ignition timing determining section 64, thecorrected ignition timing IG_(t) is determined by making a correctionusing the correction coefficient parameterizing the reference deliveryratio L_(O) and the engine speed N_(E) and is outputted to the ignitiontiming determining section 41.

When a signal for suspending ignition is inputted from theinjection/ignition determining section 54 to the above correctedignition timing determining section 64, the determination of ignitiontiming is not performed. On the other hand, a signal for instructingignition during the suspending control is inputted from theinjection/ignition determining section 54 to the corrected ignitiontiming determining section 64, IG_(t) is set to the ignition timing atthe minimum load on the suspending line and an ignition timingcorrection coefficient K_(Mt) for correcting the ignition timing at thesuspending control is read from the injection timing correcting section65. The final injection timing is obtained by correcting the aboveignition timing IG_(t) by this correction coefficient K_(Mt) (IG_(t)+K_(Mt)) and this value is outputted to the ignition timing determiningsection 41. The ignition timing at the minimum load on the suspendingline has been stored beforehand as the data parameterizing the enginespeed N_(E).

In the ignition timing correcting section 65, the ignition timingcorrection coefficient K_(Mt) as shown in FIG. 14 is determined withrespect to the number of suspendings which is inputted from thesuspending control judging section 61 beforehand by experiments andother means and this correction coefficient is read by the correctedignition timing determining section 64.

Next, the suspending control of fuel injection and spark ignition whichis executed by the ECU 60 will be described according to a flowchartshown in FIG. 12.

After determining the load index X at S103, at S201 if it is judged thatthe cycle is an initial cycle (i=0) of the suspending control for thecylinder (#k cylinder: k=1, 2 and 3), the program goes to S203 where theoperator dk (0) for the initial cycle is set to 0 and then the programskips to S302.

On the other hand, at S201 if it is judged the cycle is not an initialcycle (i≠0), the program goes to S202 where the operator d_(k) (i) forthe "i"th cycle of the #k cylinder is calculated and steps to S204. AtS204, if d_(k) (i)≦0, the program goes to S302 and if d_(k) (i)>0 goesto S301.

If the program goes from S203 or S204 to S302, in the injection amountdetermining section 62 and the injection amount correcting section 63,the fuel injection amount T_(i) at the start of the suspending iscorrected by the increment correction coefficient K_(MS) and at the sametime, in the corrected ignition timing determining 64 and the ignitiontiming correcting section 65, the ignition timing IG_(t) at the start ofthe suspending is corrected by the ignition timing correctioncoefficient K_(Mt). After that, the program goes to S205 in which asignal for injecting fuel at that cycle e ("i"th cycle of the #kcylinder) is outputted from the injection/ignition determining section54 to the injection amount determining section 62 and the correctedinjection timing determining section 38 and at the same time a signalfor instructing ignition at that cycle ("i"th cycle of the #k cylinder)is outputted to the corrected ignition timing determining section 64.Then, at S206 the indicator M_(k) of the #k cylinder is set to 1.

On the other hand, if the program steps from S204 to S301, the number ofsuspending is counted therein and then at S207 a signal for suspendinginjection in that cycle ("i"th cycle of the #k cylinder) is outputtedfrom the injection/ignition determining section 54 to the injectionamount determining section 62 and the corrected injection timingdetermining section 38 and at the same time a signal for suspendingignition also in that cycle ("i"th cycle of the #k cylinder) isoutputted to the corrected ignition timing determining section 64. Then,at S208 the indicator M_(k) of the #k cylinder is set to 0. The numberof suspending is cleared out when the program gets out of the routine.

After the setting of M_(k) is finished at S206 or S208, the programsteps to S209 where the cycle number i of the #k cylinder is counted up.Hereinafter, steps are taken in the same manner as described in thesecond embodiment.

Thus, according to the third embodiment, when the suspending control isapplied, since cycles without combustion or cycles with scavenging onlyare inserted intermittantly, the combustion chamber is rather cooled,which contributes to poor combustion. To compensate this phenomenon, theair-fuel ratio is shifted slightly to the rich side (a slight increaseof fuel injection amount) and the ignition timing is also slightlyadvanced. That is to say, the feature of the third embodiment is to keepcombustion in the good condition as well as to ensure the same effect asdescribed in the second embodiment.

It is needless to say that the aspect of this third embodiment can beapplied to the first embodiment. Further, concerning the way ofcorrecting the fuel injection amount and the ignition timing, in thethird embodiment, the preferred way of correcting both has beendescribed, however other ways of correcting either fuel injection orignition may be allowed.

FIG. 15, FIG. 16 and FIG. 17 indicate a fourth embodiment according tothe present invention. The feature of the fourth embodiment is to detectthe presence of misfire and to make the suspending conditions mapvariable based on the detection of misfire.

Referring to FIG. 15, numeral 70 denotes a three cylinder two cyclein-cylinder engine in which a cylinder pressure sensor 14 for detectingthe pressure in the cylinder is disposed in the combustion chamber inaddition to the compositions of the third embodiment. The cylinderpressure sensor 14 is connected with the input interface 24 of the ECU71.

In the cycle control of the ECU 71, it is judged whether or not misfireoccurs based on signals derived from the crank angle sensor 11 and fromthe cylinder pressure sensor 14. If misfire occurs, the predeterminedarea where misfires tend to occur is expanded by a certain degree to thehigher side of the engine load. If the target engine load is located inthat area, the frequency of suspendings is determined independently foreach #1, #2 and #3 cylinder such that the frequency of suspendings isreduced as the engine load becomes higher and a signal is outputted tothe fuel injection and ignition systems so as to suspend combustionsbased on the frequency. Further, the number of suspendings is countedfor each cylinder and in the combustion cycle the fuel injection amountand the ignition timing are corrected according to this number ofsuspendings. Further, signals of the corrected injection amount and thecorrected ignition timing are outputted to the fuel injection andignition systems to drive the fuel injector 6 and the ignitor 9respectively.

In order to realize the above cycle control, the ECU 71 mainly comprisesan engine speed calculating section 31, a crank position detectingsection 52, a misfire judging section 72, a suspending starting pointdetermining section 73, an operating condition detecting section 33, asuspending control judging section 61, a suspending conditions map 74,an injection/ignition determining section 75, an injection amountdetermining section 62, an injection amount correcting section 63, acorrected injection timing determining section 38, a corrected ignitiontiming determining section 64, an ignition timing correcting section 65,an injection timing determining section 40, an ignition timingdetermining section 41 and the driver sections 42, 43.

The misfire judging section 72 is for detecting an existence ornon-existence of misfire based on the crank angle signal from the crankangle sensor 11 and the signal from the cylinder pressure sensor 14.Namely, a misfire is detected using the phenomenon that when a misfireoccurs, the cylinder pressure becomes lower than that at the normalcombustion. The detection of misfire is done during the suspendingcontrol as well as during the normal cycle control (the control of notsuspending fuel injection and ignition).

The above suspending conditions map 74 is a map parameterizing theengine speed N_(E) and the engine load and it is prepared beforehand byexperiments and the like. The reference suspending line is establishedat the position slightly higher (to the higher load side) than theposition where misfire starts to occur. The area lower than thereference suspending line is an area where the suspending control is tobe applied.

Further, in the suspending starting point determining section 73, when amisfire signal is inputted from the misfire judging section 72, theabove reference suspending line of the suspending conditions map 74 isshifted by a predetermined value to the high load side so as to expandthe area where the suspending control is to be performed in the highload direction. On the other hand, when there is no misfire signal fromthe above misfire judging section 72, the present suspending line of thesuspending conditions map 74 is moved step by step by a predeterminedvalue toward the low load side (a lower limit is the referencesuspending line) so as to return the area where the suspending controlis to be performed in the low load direction.

In the injection/ignition determining section 75, it is determined basedon a signal from the suspending control judging section 61 whether thepresent cycle is let be a combustion cycle or a suspending cycleindependently for each #1, #2 and #3 cylinder and that determinationsignal is outputted to the injection amount determining section 62, thecorrected injection timing determining section 38 and the correctedignition timing determining section 64. Further, the above signal ofsuspending combustions is inputted to the misfire judging section 72 todiscriminate between misfires and suspendings (artificial misfires).

Next, the determination of the suspending line (suspending startingpoint) will be described with reference to a flowchart in FIG. 17.

When the program starts, at S401 the cylinder pressure of the objectcylinder is detected based on a signal derived from the cylinderpressure sensor 14 and then at S402 it is judged whether or not thedetected cylinder pressure is a pressure indicating a misfire by a crankangle signal derived from the crank angle sensor 11 and by a signalshowing that the present cycle is a combustion cycle.

If it is judged that the cylinder pressure is a pressure indicating amisfire, namely that a misfire has occurred, the program goes to S404and if it is judged that no misfire has occurred, the program returns toS401. When the program goes to S404 as a result of judging that amisfire has occurred, the suspending line (suspending starting point) ofthe suspending conditions map 74 is raised by a predetermined valuetoward the high load side and then at S405 it is judged whether or not amisfire has occurred again in a following predetermined few cycles.

If a misfire has occurred in the predetermined few cycles, the programreturns to S404 further to raise the suspending starting point. On theother hand, if a misfire has not occurred in the predetermined fewcycles, the program steps to S406 where the suspending starting point isreduced by a predetermined value toward the low load side.

Further, at S407 it is judged whether or not the suspending startingpoint thus reduced has returned to the reference suspending line. Ifnot, the program returns to S405 and if yes, the program gets out of theroutine.

The cycle control is processed based on the suspending conditions map 74which has been obtained as described above.

According to the fourth embodiment, the suspending starting point of thesuspending conditions map is determined in an optimum style with respectto an individual engine regardless of production variations of theengine, aged deteriorations of s specific engine and the like and as aresult an optimum suspending control can be accomplished for any engine.

The fourth embodiment is a variation of the third embodiment, however itis needless to say that the aspect of the fourth embodiment can beapplied also to the first and second embodiments.

Next, FIG. 18, FIG. 19, FIG. 20 and FIG. 21 show an example of a fifthembodiment according to the present invention. The fifth embodiment is avariation of the third embodiment which is constituted such that thefuel properties are detected and based on that fuel property thesuspending conditions map is made variable.

Referring now to FIG. 18, numeral 80 denotes a three cylinder two-cyclein-cylinder injection engine in which in addition to the enginecomponents described in the third embodiment a fuel properties sensor (asensor for detecting fuel properties, in this embodiment, a degree offuel gravity) 15 is disposed in the fuel delivery line of the engine 80.The fuel properties sensor 15 is connected with the input interface 24of the ECU 81.

In the cycle control by the ECU 81, the area where misfires tend tooccur has been determined based on the standard fuel properties and thatarea has been established on a map which will be described hereinafter.The area is varied according the fuel properties detected by the fuelproperties sensor 15. When the target engine load is located in the areaof this map, the frequency of suspending combustions is determinedindependently for each #1, #2 and #3 cylinder based on the engine speedand the engine load so as to reduce that frequency as the engine loadbecomes high. After thus determined frequency is converted into asignal, the signal is outputted to the fuel injection and ignitionsystems to suspend fuel injection and spark ignition for that cycle. Onthe other hand, the number of suspending has been counted independentlyfor each cylinder and in the next combustion cycle the fuel injectionamount and the ignition timing are corrected in accordance with thatnumber of the previous suspendings. The corrected fuel injection amountand the corrected ignition timing are converted into signalsrespectively and those signals operate the fuel injection and ignitionsystems so as to drive the injector 6 and the ignitor 9.

In order to realize the above cycle control as depicted in FIG. 19, theECU 81 mainly comprises an engine speed calculating section 31, a crankposition detecting section 52, a fuel properties judging section 82, asuspending starting point determining section 83, an operating conditiondetecting section 33, a suspending control judging section 61, asuspending conditions map 84, an injection/ignition determining section54, an injection amount determining section 62, an injection amountcorrecting section 63, a corrected fuel injection timing determiningsection 38, a corrected ignition timing determining section 64, anignition timing correcting section 65, an injection timing determiningsection 40, an ignition timing determining section 41 and the driversections 42, 43.

The above suspending conditions map 84 is a map parameterizing theengine speed N_(E) and the engine load, and it has been preparedbeforehand by experiments and the like. The suspending line, namely thesuspending starting line which determines the starting point ofsuspending combustions is established when combustion is normal and thefuel has a standard fuel properties. The final suspending line on themap is set slightly at the high load side so as vary according to thesuspending starting point determining section 83. The load area belowthis suspending line is an area where the fuel injection and ignitionare suspended.

Further, the above fuel properties judging section 82 is for finding afuel property of the employed fuel based on a signal from the fuelproperties sensor 15.

Further, based on a signal from the fuel properties judging section 82,the above suspending starting point determining section 83 detectswhether or not there occurs a change in the fuel properties. If a changeoccurs in the fuel properties, a degree of changing the suspendingstarting line of the suspending conditions map 84 is obtained byretrieving a map and the suspending starting line is made to be changed.This map has been obtained beforehand by experiments and the like and ithas such a characteristic shown in FIG. 21 that the suspending startingpoint moves toward the high load side as the fuel properties movestoward the heavy side.

Next, the determination of the suspending starting point of thesuspending conditions map 84 will be described according to theflowchart in FIG. 20.

When the program starts, at S501 the fuel properties are detected basedon a signal from the fuel properties sensor 15 and then at S502 it isjudged whether the fuel is a heavy or light fuel. Next, the program goesto S503 where it is judged whether or not there is a change in the fuelproperties. If there is not, the program returns to 501 and if there isa change, the program goes to S504 where a degree of change of thesuspending starting point is obtained by referring to the predeterminedmap as shown in FIG. 21 and then at S505 the suspending starting pointof the suspending conditions map 84 is changed. Thus, the cycle controlis performed based on the suspending conditions map 84 which has beenthus obtained.

According to the fifth embodiment, since the suspending control iscorrected according to the change of fuel properties, the stablecombustion in the low load condition can be obtained regardless of thefuel properties of the employed fuel. The fifth embodiment has beendescribed with relation to the third embodiment but the aspect thereofcan be applied also to the first, second and fourth embodiments. FIG.19A shows the aspect of the fifth embodiment applied to the fourthembodiment.

In summary, according to the present invention, it is possible to applyan effective combustion control to an actual two cycle in-cylinderinjection engine without making large modifications. Further, thepresent invention provides an effective way of the combustion controlfor a multi-cylinder two cycle engine. Furthermore, according to thepresent invention, the stable combustion in the low load condition canbe attained even when the engine is deteriorated or when the fuelproperties are changed.

While the presently preferred embodiments of the present invention havebeen shown and described, it is to be understood that these disclosuresare for the purpose of illustration and that various changes andmodifications may be made without departing from the scope of theinvention as set forth in the appended claims.

What is claimed is:
 1. A control system for a two cycle direct fuelinjection engine having, a fuel injector inserted into a cylinder ofsaid engine for directly injecting an amount of fuel therein, an igniterelectrically connected to a spark plug via an ignition coil for ignitingsaid fuel in said cylinder, a throttle sensor mounted on said engine fordetecting an opening degree (α) of a throttle valve and for generating athrottle signal indicative thereof and engine r.p.m. calculating meansresponsive to a crank angle signal from a crank angle sensor attachednear a crankshaft of said engine for calculating an engine speed and forproducing an engine speed signal indicative thereof, comprising:targetload detecting means, responsive to said throttle signal and said enginespeed signal, for calculating a target load required by a driver and forproducing a load signal indicative thereof; suspending decision means,responsive to said engine speed signal and said load signal, for judgingwhether said target load is within a suspending region and, when saidtarget load is within said suspending region, for generating asuspending signal indicative thereof; suspending frequency determiningmeans, responsive to said suspending signal, for determining a firstfrequency and a second frequency different from said first frequency ofsuspending fuel injection and fuel ignition in accordance, respectively,with first and second target loads in said suspending region and forgenerating a control signal indicative thereof; and control meansresponsive to said control signal for controlling said fuel injector andsaid igniter, wherein in response to a signal indicating the presence ofmisfire, said suspending region is expanded to the high load side. 2.The control system as set forth in claim 1, further comprising:injectionamount correcting means for correcting a fuel injection amount accordingto said first frequency.
 3. The control system as set forth in claim 1,further comprising:ignition timing correcting means for correcting anignition timing according to said first frequency.
 4. The control systemas set forth in claim 1, where-insaid suspending region is variedaccording to the fuel properties.
 5. A control system for a two cycledirect fuel injection engine having, a fuel injector inserted into acylinder of said engine for directly injecting an amount of fueltherein, an igniter electrically connected to a spark plug via anignition coil for igniting said fuel in said cylinder, a throttle sensormounted on said engine for detecting an opening degree (α) of a throttlevalve and for generating a throttle signal indicative thereof and enginer.p.m. calculating means responsive to a crank angle signal from a crankangle sensor attached near a crankshaft of said engine for calculatingan engine speed (N) and for producing an engine speed signal indicativethereof, comprising:target load detecting means, responsive to saidthrottle signal and said engine speed signal, for calculating a targetload required by a driver and for producing a load signal indicativethereof; suspending decision means, responsive to said engine speedsignal and said load signal, for judging whether said target load iswithin a suspending region and, when said target load is within saidsuspending region, for generating a suspending signal; suspendingfrequency determining means, responsive to said suspending signal, fordetermining for each cylinder of said engine a first frequency and asecond frequency different from said first frequency of suspending fuelinjection and spark ignition in accordance, respectively, with first andsecond target loads in said suspending region and for generating acontrol signal indicative thereof; and control means responsive to saidcontrol signal for controlling said fuel injector and said igniter,wherein in response to a signal indicating the presence of misfire, saidsuspending region is expanded to the high load side.
 6. The controlsystem as set forth in claim 5, further comprising:injection amountcorrecting means for correcting a fuel injection amount according tosaid first frequency.
 7. The control system as set forth in claim 5,further comprising:ignition timing correcting means for correcting anignition timing according to said first frequency.
 8. The control systemas set forth in claim 5, where-insaid suspending region is variedaccording to the fuel properties.
 9. A control method for a two cycledirect fuel injection engine having, a fuel injector inserted into acylinder of said engine for directly injecting an amount of fueltherein, an igniter electrically connected to a spark plug via anignition coil for igniting said fuel in said cylinder, a throttle sensormounted on said engine for detecting an opening degree (α) of a throttlevalve and for generating a throttle signal indicative thereof and enginer.p.m. calculating means responsive to a crank angle signal from a crankangle sensor attached near a crankshaft of said engine for calculatingan engine speed and for generating an engine speed signal indicativethereof, comprising:calculating a target load required by a driver inresponse to said throttle signal and said engine speed signal; judgingwhether said target load is within a suspending region; determining afrequency of suspending fuel injection and fuel ignition in accordancewith said target load when judged within said suspending region, varyingsaid frequency according to a change of target load which remains withinsaid suspending region; controlling fuel injection and fuel ignitionaccording to said frequency; and in response to a signal indicating thepresence of misfire, expanding said suspension region to the high loadside.
 10. The control method as set forth in claim 9, further comprisingthe step of:correcting a fuel injection amount according to said firstfrequency.
 11. The control method as set forth in claim 9, furthercomprising the step of:correcting an ignition timing according to saidfirst frequency.
 12. The control system as set forth in claim 9,where-insaid suspending region is varied according to the fuelproperties.
 13. A control method for a two cycle direct fuel injectionengine having, a fuel injector inserted into a cylinder of said enginefor directly injecting an amount of fuel therein, an igniterelectrically connected to a spark plug via an ignition coil for ignitingsaid fuel in said cylinder, a throttle sensor mounted on said engine fordetecting an opening degree (α) of a throttle valve and for generating athrottle signal indicative thereof and engine r.p.m. calculating meansresponsive to a crank angle signal from a crank angle sensor attachednear a crankshaft of said engine for calculating an engine speed and forgenerating an engine speed signal indicative thereof,comprising:calculating a target load required by a driver in response tosaid throttle signal and said engine speed signal; judging whether saidtarget load is within a suspending region; determining for each cylinderof said engine a frequency of suspending fuel injection and fuelignition in accordance with said target load when judged within saidsuspending region, varying said frequency according to a target loadchange which remains within said suspending region; controlling fuelinjection and fuel ignition according to said frequency; and in responseto a signal indicating the presence of misfire, expanding saidsuspending region to the high load side.
 14. The control method as setforth in claim 13, further comprising the step of:correcting a fuelinjection amount according to said first frequency.
 15. The controlmethod as set forth in claim 13, further comprising the stepof:correcting an ignition timing according to said first frequency.